This invention relates to linkage means for an implement, and more particularly, to linkage means for controlling movement of a tree harvester head.
In a known system, a boom is pivotally mounted relative to a vehicle, with a stick arm in turn pivotally mountd to the boom, and a tree harvester head pivotally mounted to the end of the stick arm. A cylinder interconnects the vehicle and boom for raising and lowering the boom, and a cylinder interconnects the boom and stick arm for providing relative movement therebetween. yet another cylinder has one end pivotally connected relative to the stick arm, and the other end extends to a pair of links operatively connected with the tree harvester head so that actuation of this cylinder moves the tree harvester head relative to the stick arm.
It has been found that, in such a system, once the attitude of the tree harvester head is chosen by appropriate manipulation of the controls of the cylinders, extension and retraction of only the cylinder interconnecting the boom and stick arm results in a variation in the attitude of such tree harvester head. In order to avoid such a change in attitude, actuation of the cylinder interconnecting the stick arm and tree harvester head is necessary.
It is to be understood that, under certain conditions, it would be desirable that the tree harvester head maintain a certain approximate attitude as chosen even though the stick arm is moved relative to the boom, avoiding the necessity of actuating the cylinder interconnecting the stick arm and tree harvester head to maintain a chosen tree harvester head attitude.
Of general interest in this area is U.S. Pat. No. 2,870,924 to Wills, including a boom, a stick arm, a bucket, and cylinders operatively associated therewith.